Disk-shaped object of synthetic thermoplastic material, and method for producing same

ABSTRACT

A disk-shaped object of synthetic thermoplastic material has contact surfaces on opposite sides that possess a rough texture. In a method for production of the disk-shaped object, synthetic material is injected under pressure in a plasticized state into a cooled molding tool and removed therefrom after a cooling phase, the molding tool having correspondingly rough molding surfaces to form the rough contact surfaces of the object.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of German Patent Application10307108.3 filed 19 Feb. 2003 and German Patent Application102004004701.4 filed 29 Jan. 2004, both of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a disk-shaped object of syntheticthermoplastic material and to a method for producing the same.

[0003] Disk-shaped objects are employed, for example, as an intermediatebetween structural parts to seal them off from one another and/orconnect them adhesively to one another. Examples of such applicationsare disclosed in GB 2,067,253 A and EP 0,504,957 A2. In theseapplications, a disk-shaped object is arranged between parts to beconnected and then brought into a flowable state by heating, so that thedisk-shaped object will adhesively connect the two parts to one anotherand possibly penetrate gaps between the parts to seal them tight.

[0004] In the production and assembly of disk-shaped objects of the kindspecified, various problems have arisen. The objects have been difficultto remove from the recess of a molding tool. Objects of annular shapeespecially have also exhibited a marked ill-defined warping andshrinking behavior, so that prescribed dimensions have failed to bereliably attained. Furthermore, individual objects when transported inbulk have tended to stick together, interfering considerably withindividual use, especially in automatic assembly. Experiments with asuitable liquid as parting agent, to prevent the individual objects fromsticking together, have failed to yield satisfactory results.

BRIEF DESCRIPTION OF THE INVENTION

[0005] Accordingly, an object of the invention is so to configuredisk-shaped objects of the kind specified so that they are easilyisolated and assembled.

[0006] Another object of the invention is to improve a process ofproduction of such objects, to alleviate unmolding problems and toprevent warping and shrinking of the objects.

[0007] According to the invention, contact surfaces provided on oppositesides of a disk-shaped object of synthetic thermoplastic material aremade rough. Surprisingly, it has been found that with a rough conditionof the contact surfaces, adjacent disk-shaped objects no longer have thetendency to stick together, but are easily separated and isolated fromeach other. No additional parting agents are required. Mechanical meansof automatically isolating and assembling the objects formed accordingto the invention can therefore be operated without trouble.

[0008] By a process according to the invention, suitable roughness ofthe contact surfaces is generated in the forming of the objects. Moreparticularly, molding surfaces of a molding tool forming the contactsurfaces are provided with a roughness matching the desired contactsurfaces of the objects. Due to the roughness, a disk-shaped object isbetter secured in the tool, and disadvantageous shrinking and warpingeffects are avoided. Further, it has been found that by opening themolding tool prior to complete cooling, slight residual shrinkage, stillto occur, favors the parting of object and tool, considerablyfacilitating the unmolding and ejection of the object from the moldingtool. Deformations of the object, caused by the unmolding operation, areavoided in this way.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention will be further described in conjunction with theaccompanying drawings, which illustrate preferred (best mode)embodiments, and wherein:

[0010]FIG. 1 shows a perspective representation of a disk-shaped objectaccording to the invention;

[0011]FIG. 2 shows a cross-section of a molding tool for producing anobject according to the invention; and

[0012]FIG. 3 shows the use of a disk-shaped object according to theinvention for tight connection of two structural parts.

DETAILED DESCRIPTION OF THE INVENTION

[0013] In one embodiment according to the invention, an object 1 shownin FIG. 1 is in the form of a circular disk having two parallel circularfaces, forming contact surfaces 2, 3. The disk has a diameter of about15 mm and a thickness of about 1 mm, for example. In the center of theobject 1, there is a square through-hole 4. The diagonal dimension ofthe hole 4 is smaller than the outside diameter of the object 1, ofcourse. A disk-shaped object in accordance with the invention may have anon-circular contour and may have a non-square hole.

[0014] The object 1 is made of a thermoplastic adhesive that can bebrought into a flowable state by heating. At a temperature of about 20°C., for example, the material of the object 1 is solid, not completelyrigid but elastically deformable. Such an adhesive of polyamide isobtainable under the trade designation Thermelt by the firm of BostikFindley GmbH, 33829 Borghausen. Using this known adhesive, theadvantages of the invention have appeared with especial clarity.

[0015] The object 1 is intended for use as an intermediate betweenstructural parts connectable to one another. For such use, it may benecessary to produce a considerable number of objects 1, which are thentransported to a place of use, more or less in bulk, in suitablereceptacles. Then, the objects 1, as delivered, must be individually fedin an assembling operation. In order for such use to be easily andquickly accomplished, by automatic means if required, the contactsurfaces 2, 3 of the objects 1 are provided with a rough surfacetexture. Due to the roughness of the contact surfaces 2, 3, the objects1, even if the synthetic thermoplastic material is fairly soft, have notendency to adhere to each other, so that they are easily separated.

[0016] The production of an object 1 of thermoplastic adhesive ispreferably performed by an injection molding process. Under heat andpressure, plasticized synthetic adhesive is injected into moldingrecesses of a cooled molding tool. After a cooling phase, the moldingtool is opened and an object, meanwhile solidified, is removedtherefrom.

[0017] In FIG. 2, a suitable molding tool 10 is represented in section.It comprises a bottom tool half 1 1 having a recess 12 matching theshape of the object 1 and an upper tool half 13 closing the recess 12.In the upper tool half 13, a supply passage 14 is provided for feedingthe plasticized adhesive.

[0018] In order to generate the rough texture of the contact surfaces 2,3 during the actual production of an object 1, the matching moldingsurfaces 15, 16 of the tool halves 11, 13 are provided with a roughsurface of corresponding roughness depth. The roughness of the surfacesof the tool halves 11, 13, of a high-strength steel, for example, mayadvantageously be generated by spark erosion.

[0019] The roughness of the molding surfaces 15, 16 of the molding tool10, besides generating rough contact surfaces 2, 3, has the surprisingadvantage that after injection of the adhesive into the molding tool 10,the object 1 is preserved in its preassigned shape during cooling, anddoes not tend to shrink or warp in an undesired manner. After awell-defined cooling phase in which the object 1 has attained a solidstate, though without having been completely cooled as yet, the moldingtool is opened by taking off the tool half 13. During cooling thatcontinues after the molding tool has been opened, the object 1 shrinksslightly and, due to the roughness of the surfaces of object 1 and toolhalf 11 in contact with each other, the object 1 detaches itself fromthe tool half 11 automatically, so that it can easily be removed orejected from the recess 12 of the molding tool 10.

[0020] For the purpose of the invention, an averaged German Standard DIN4768 roughness depth R_(z) of the corresponding surfaces of the objectand of the molding tool from 40 to 100μ is especially suitable.Preferably, the average roughness depth lies in the range from 55 to70μ. Suitable arithmetic mean rugosities R_(a) lie in a range from 6 to25μ, preferably in a range from 10 to 15μ, such as 12.5μ.

[0021] The averaged roughness depth R_(z) designates the mean rugosityof five reference segments within an evaluation length. The arithmeticmean rugosity R_(a) is the arithmetic mean of the absolute values of theprofile deviations within a reference segment.

[0022]FIG. 3 shows a preferred application of the disk-shaped object 1.In this application, the object 1, as shown in the left-hand half of therepresentation in FIG. 3, is mounted between a plate-like part 20 andthe flange 21 of a fastening element 22 inserted in an opening of thepart 20, for example a bodywork sheet. In the form shown, the fasteningelement 22 comprises spring locking elements 23, bearing on the side ofthe substrate 20 away from the flange 21 and pressing the fasteningelement 22 against the object 1 and the part 20. The arrangement,preassembled in this way, is then heated, in an oven, for example, tosuch an extent that the thermoplastic adhesive of which the object 1 isconstituted becomes flowable. In a flowable state, the object 1 iscompressed by the contact force of the locking elements 23, as indicatedin the right-hand half of the representation in FIG. 3. Thus, the flange21 is drawn into contact with the part 20, the material of the object 1flowing into the annular gap between the opening and the fasteningelement 22, and sealing it completely. By the adhesive action of thethermoplastic adhesive of the object 1, moreover, the load capacity ofthe connection between fastening element 22 and part 20 is enhanced.

[0023] While preferred embodiments of the invention have been shown anddescribed, it will be apparent that modifications can be made withoutdeparting from the principles and spirit of the invention, the scope ofwhich is defined in the appended claims.

What is claimed is:
 1. Disk-shaped object of synthetic thermoplasticmaterial, such as thermoplastic adhesive, for use as an intermediatebetween parts, has contact surfaces on opposite sides of the object thatare rough, wherein their averaged roughness depth R_(x) lies in a rangefrom 40 to 100μ.
 2. Object according to claim 1, wherein the averagedroughness depth R_(z) of the contact surfaces lies in the range from 55to 70μ.
 3. Object according to claim 1, wherein the arithmetic meanrugosity R_(a) lies in a range from 6 to 25μ.
 4. Object according toclaim 2, wherein the arithmetic mean rugosity R_(a) lies in a range from10 to 15μ.
 5. Method of producing a disk-shaped object according to anyone of the preceding claims, wherein the synthetic material is injectedunder pressure in a plasticized state into a cooled molding tool andremoved therefrom after a cooling phase, and wherein molding surfaces ofthe molding tool form the contact surfaces of the object and aretextured with a roughness depth equivalent to that of the contactsurfaces.
 6. Method according to claim 5, wherein opening of the moldingtool takes place prior to the complete cooling of a disk-shaped objectcontained therein.